1. Field of the Invention
The present invention relates to novel polyamide copolymers (hereafter sometimes simply referred to as polyamides) having excellent resistance to hydrolysis, low temperature characteristics (low temperature softness), heat aging resistance and mechanical properties and also having excellent efficiency in processabilities and transparency.
2. Prior Art Statement
Polyester polyamide copolymers obtained by reacting organic diisocyanates with dicarboxylic acids and methods for production thereof are already known as described in, for example, U.S. Pat. Nos. 4,087,481, 4,129,715 and 4,156,065, etc. It is well known that softness, elastic properties, mechanical properties, oil and chemical resistance and heat resistance are good in these copolymers.
However, these conventional polyester polyamide copolymers described above have poor transparency and temperature dependency of melt viscosity thereof is great and therefore, it was difficult to apply molding as in other general purpose thermoplastic resins to these copolymers. In addition, with these conventional polyester polyamide copolymers, problems also arise in resistance to hydrolysis and heat aging resistance.
For example, when polyester polyamide copolymers having a poor resistance to hydrolysis are prepared into films, their surfaces tend to be sticky in a relatively short period of time or cause cracking. Accordingly, the polyester polyamide copolymers are considerably limited upon use. The polyester polyamide copolymers of this kind have a limit in improving resistance to hydrolysis since they contain ester groups in more than a certain degree. On the other hand, the use of polyethers in place of polyesters results in extremely poor resistance to oxidative aging while resistance to hydrolysis is improved.
An object of the present invention is to provide novel polyamide copolymers having improved processabilities, transparency, resistance to hydrolysis, low temperature characteristics and heat aging resistance, without injuring the excellent heat resistance and mechanical properties of conventional polyester polyamide copolymers.